The present invention relates to insulative coating compositions for insulating stacked laminations used in electromechanical hardware, such as rotors and stators in electrical motors and generators, and a method of making rotors and stators for use in electric motors and generators using these coatings.
Electrical components such as rotors and stators for motors and generators are typically manufactured from a plurality of thin steel laminations which are stacked together to form the rotor or stator. Treating each lamination with an insulative coating reduces the eddy current losses inherent in motors and generators. Some chemical compounds that have been commonly used for such insulative coatings include those made from aluminum chromate and containing hexavalent chromium. These are environmentally unsafe and hazardous to personnel involved in manufacturing the components. Accordingly, workplace exposure to hexavalent chromium is strictly limited by regulation and further regulations concerning air and water levels of chromium compounds have been issued or are expected to be issued.
Solutions of magnesium methylate in methanol are known to be effective in forming thin insulative coatings. See, for example, Suchoff, U.S. Pat. No. 2,796,364. Magnesium methylate is believed to be free of the health and safety risks associated with hexavalent chromium compounds. Applying a solution of magnesium methylate in an organic solvent to a metal surface and heating the surface to evaporate the solvent produces a thin coating of magnesium oxide on the surface of the metal. A thicker coating would result in improved electrical insulation between the laminations, and in a corresponding reduction in eddy current losses. There is a need for thicker, more effective magnesium methylate coatings, which would provide improved reduction in eddy current losses in motor and generator rotors and stators, compared to prior art coatings. There is also a need to avoid the health and safety risks associated with other coatings, such as hexavalent chromium compounds.
According to one aspect of the present invention, a coating composition includes magnesium methylate, methyl alcohol, silica and talc. The coating can also include a wetting agent, such as a nonionic, phosphate surfactant. The composition may include methyl alcohol, and magnesium methylate in a concentration up to ten percent by weight. The composition may also include silica in a concentration up to 15% by weight, and talc in a concentration up to 25% by weight. It is also advantageous to add a small amount of wetting agent, in order to ease the preparation of the coating, in an amount not exceeding 1% by weight.